Ventilated fuse.



E. M. HEWLETT.

VENTILATED FUSE.

APPLIGATIOH FILED AUG. 26, 1909.

Patanted Jan. 25, 1910.

In vcntor. Edward/4 Herr/e111,, By plaw r Att Witnesses:

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EDWARD M. HEWLETT, OE SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

VENTILATEID FUSE.

Specification of Letters Patent.

Patented Jan. 25, 1910.

Application filed August 26, 1909. SerialNo. 514,681.

1' 0 all whom it may concern:

Be it known that I, EDWARD M. HEWLETT, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Ventilated Fuses, ofWhich the following is a specification.

This invention relates to thermal cut-outs or fuses for electriccircuits of the type in which a wire of low melting point gives wayunder the heating action of a current passing through it whenever suchcurrent exceeds a predetermined value. When fuses of this type are usedon circuits of high voltage and large amperage, an arc is formed betweenthe ends of the ruptured fuse wire, and some means must be provided forextinguishing this are. One way of doing this is to cause the gases andvapors developed by the are to be expelled away from the fuse conductorwith sufficient force to snap the arc. My invention has especialreference to fuses of this expulsion type, such, for instance, as theone shown in the patent to (I. E. Eveleth, dated March 27, 1900, No.816,443.

In this device the fuse-wire is incloscd in a casing which comprises anenlarged chamher and an open-ended tube extending there from. Thefuse-wire is stretched through both portions of the casing, and when itgives way under the stress of an excessive current, the resulting gasesand vapors create a pressure in the chamber which causes a prolongedblast through the tube, thereby efl'ectually blowing out the arc.

The value of a fuse depends largely upon its carrying the current up toa prcdetermined value without giving way. Its breaking point is afunction of the temperature to which it is raised by the heating effectof the current. This clfcct is intensitied in fuses of the Eveleth type,by the enveloping casing, which comprises the hot air within it andtends to produce a rupture of the fuse-wire before the current rises tothe predetermined voltage.

The object of my invention is to prevent this abnormal heating of thefusewire, and I accomplish this by arranging the casing with its openend uppermost, and )roviding an inlet for air near the lower on of thecasing, so that there may be a circulation of air up through the casing.The fuse-Wire l I t l i l l will be kept thus in an. atmosphere which isat a normal temperature, and premature melting will be obviated.

The accompanying drawing is a longitfudinal section of one form of myventilated use.

The chamber 1 is preferably in the form of a bulb, and is made of metaladapted to Withstand the pressure of the explosion of the gasesdeveloped by the blowing of the fuse. The bulb is covered on its outersurface with a coating of insulating compound 2. The tube 3 is composedof non-inflammable insulating material such as indurated fiber. Onecontact blade 4 is secured to the tube and a second blade 5 is attacheddirectly to the bulb. The fusestrip 6 is at.- tached to a screw-plug 7,which is screwed into a threaded opening at the lower end of the bulb,adjacent to the contact blade 5 and in line with the tube. The fuse runsup through the bulb and the tube and its upper end is bent over the edgeof the tube and secured to the contact blade 4. The strip 6 may benarrowed at S to cause the rupture to begin in the chamber.

At some convenient point in the bulb an opening 9 is made, to serve asan inlet for air. Means are provided for automatically closing thisopening when the fuse blows, in order to prevent the escape of flametherethrough. I prefer to use an ordinary check valve 10 arrangedpreferably in a pipe 11 screwed into the opening 9, and containing alsoan annular seat 12 against which the valve seats. By giving the pipe anoblique upward direction and hinging the valve at its upper edge, itwill hang vertically, as shown, keeping the pipe partially open for thefree admission of air, but being in a good position to be caught andclosed by the rush of gas when the fuse blows, and thus prevent theescape of tire through the air inlet. A nozzle 13 of fiber or the likeconfines any flame. which may momentarily shoot out as the valve closes.

Under normal conditions the heat developed by the fuse in the bulb andtube causes an upward current of air therein, fresh air entering throughthe pipe. Tn this way the temperature of the air in the casing isprevented from rising above normal, and premature explosion of the fuseis avoided. When the fuse does blow, the automatic closing of the valvecompels the blast to take place throu h the tube as in the case of thestandard veleth fuse.

In accordance with the provisions of the patent statutes, I havedescribed the principle of operation of m invention, together with theapparatus w ich I now consider to represent the best embodiment thereof;but I desire to have it understood that the apparatus shown is onlyillustrative, and that the invention can be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is,-

1. In an expulsion fuse, means for ventilating said fuse under normalconditions, and means for confining the blast of exploding gases to theregion occupied by the fuse.

2. The combination with an ex ulsion fuse comprising an upright casing,aving an opening for admitting air, of means for closin said openingautomatically when the fuse b ows.

3. In an expulsion fuse, the combination with a casing open at the top,of means for admitting air to the lower part of said casing, and meansfor shutting off the air when the fuse blows.

4. A casin for an expulsion fuse, comprising a bul and a tube risingtherefrom, said bulb having an air inlet.

5. A casing for an expulsion fuse, comprising a tube, a bulb connectedtherewith and having an air inlet, and an outwardlyclosin check valvecontrolling said inlet. 6. .E casing for an expulsion fuse, comprising atube, a bulb connected therewith and having an air inlet, a pipeextending from said inlet, and an outwardly-closing check valve in saidpipe.

In witness whereof, I have hereunto set my hand this th da of August,1909.

ED'WA D M. HEWLETT.

Witnesses:

BENJAMIN B. HULL, MARGARET E. WOOLLEY.

